Regional Apparent Boundary Layer Lapse Rates Determined fromCALIPSOand MODIS Data for Cloud-Height Determination

Reliably determining low-cloud heights using a cloud-top temperature from satellite infrared imagery is often challenging because of difficulties in characterizing the local thermal structure of the lower troposphere with the necessary precision and accuracy. To improve low-cloud-top height estimates over water surfaces, various methods have employed lapse rates anchored to the sea surface temperature to replace the boundary layer temperature profiles that relate temperature to altitude. To further improve low-cloud-top height retrievals, collocatedCloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO) andAquaModerate Resolution Imaging Spectroradiometer (MODIS) data taken from July 2006 to June 2007 and from June 2009 to May 2010 (2 yr) for single-layer low clouds are used here with numerical weather model analyses to develop regional mean boundaryapparentlapse rates. These parameters are designated as apparent lapse rates because they are defined using the cloud-top temperatures from satellite retrievals and surface skin temperatures; they do not represent true lapse rates. Separate day and night, seasonal mean lapse rates are determined for 10′-resolution snow-free land, water, and coastal regions, while zonally dependent lapse rates are developed for snow/ice-covered areas for use in the Clouds and the Earth’s Radiant Energy System (CERES) Edition 4 cloud property retrieval system (CCPRS-4). The derived apparent lapse rates over ice-free water range from 5 to 9K km−1with mean values of about 6.9 and 7.2K km−1during the day and night, respectively. Over land, the regional values vary from 3 to 8Kkm21, with day and night means of 5.5 and 6.2K km−1, respectively. The zonal-mean apparent lapse rates over snow and ice surfaces generally decrease with increasing latitude, ranging from 4 to 8K km−1. All of the CCPRS-4 lapse rates were used along with five other lapse rate techniques to retrieve cloud-top heights for 2 months of independentAquaMODIS data. When compared with coincidentCALIPSOdata for October 2007, the mean cloud-top height differences between CCPRS-4 andCALIPSOduring the daytime (nighttime) are 0.04 ± 0.61km(0.10 ± 0.62 km) over ice-free water,−0.06 ± 0.85km(−0.01 ± 0.83 km) over snow-free land, and 0.38 ± 0.95km (0.03 ± 0.92 km) over snow-covered areas. The CCPRS-4 regional monthly means are generally unbiased and lack spatial error gradients seen in the comparisons for most of the other techniques. Over snow-free land, th